Catalytic reforming process



Dec" 1, 1953 Filed July 14, 1951 LA VERN H. BECKBERGER ET AL CATALYTIC REFORMING PROCESS 2 Sheets-Sheet 1 COM PR ESS ER LE 524 HEATER REACTOR S E PARATO R j INTERMEDIATE HEATER REACTOR RECYCLE GAS FlG.l

FIRED HEATER NAPHTHA FEED Lo Vern H. Beckberger Rudolph C.Woerner INVENTORS ATTORNEY Dec. 1,1953

Filed July 14, 1951 FIG.2

LA VERN H. BECKBERGER ET AL CATALYTIC REFORMING PROCESS 2 Sheets-Sheet 2 u r 2 oo 3. 8 d o w 2 S 0 3 N 9 a; 8 8 N 8 (.LVBN-WU uaswnu amu'oo LaVem H.Beckberger Rudolph C.Woerner INVENTORS ATTO R N EY Patented Dec. 1, 1953 UNITED STATES PATENT OFFICE CATALYTIC REFORMING PROCESS La Vern H. Beckberger, East Chicago, Ind., and Rudolph C. Woerner, Houston, Tex., assignors to Sinclair Refining Company, New York, N. Y., a corporation of Maine Application July 14, 1951, Serial No. 236,792

4 Claims. 1

This invention relates to catalytic reforming of petroleum hydrocarbon fractions which boil within the naphtha range and more particularly relates to improvements in catalytic reforming with a catalyst comprising molybdenum oxidealumina-silica. Reforming of various straight run naphtha fractions is commercially desirable to improve their quality as motor and aviation gasoline fuels by increasing octane number. The stocks which ordinarily are reformed comprise the heavier straight run naphtha fractions, e. g. of boiling range of about 250 to 400 F., although full range gasoline stocks or various selected fractions cut from the stock may be and often are subjected to the reforming reaction. The reforming process involves processing the charge stock under conditions of elevated temperature and pressure and, for most desirable liquid recoveries of high octane value, processing in the presence of a catalyst which selectively promotes isomerization and dehydrogenation reactions. A substantial partial pressure of hydrogen is provided, usually by tail gas recycle, to preserve catalyst onstream life and activity.

We have found in reforming with a molybdenum oxide-alumina-silica catalyst in the presence of hydrogen that the introduction of a very small proportion of oxygen with the hydrogen gas stream results in a marked shift in the relationship between the yield of useful liquid products and the octane number of the liquid product yield. The improvement, for example, may amount to'about a ,6 octane number gain at a given yield or a comparable yield increase at a given octane level.

According to our invention, a petroleum hydrocarbon fraction boiling in the naphtha range is subjected to a reforming reaction in the presence of a molybdenum oxide-alumina-silica catalyst and a hydrogen containing gas stream under conditions of a temperature between about 850 to 1000 F. but advantageously limited to the range of 890 to 950 F., a pressure in the range of about 500 to 1000 p. s. i. g., a liquid hourly space velocity of about 0.5 to 4.0 and a hydrogen to hydrocarbon feed ratio of between 2/1 and 8/1 while adding continuously about 0.001 to 0.2% by volume of oxygen to the hydrogen containing gas stream.

The oxygen may be added in the form of air or in the form of pure oxygen which is advantageous if nitrogen build-up in the system is to be avoided. We have found that the system is responsive to improvement when even trace amounts of oxygen are introduced although 0.001% represents the approximate limit of our analytical determination. The improvement appears to be linear up to about 0.1% when it levels off. Little if any improvement is noted above about 0.2% oxygen (1.0% air) and undesirable side reactions tend to commence.

Our discovery appears to be specifically associated with molybdenum oxide-alumina reform ing catalysts which contain minor proportions of silica. A typical catalyst of value is the commercially available catalyst of the Harshaw Chemical Company, M0 0201, which comprises in typical analysis: A12O3=83.80%, M002=10.14%, Si02=5.04%, volatile matter=l2.8% at 1600 F., volatile matter=4.5% at 900 F. and carbon=l.80%. Other known molybdenum oxidealumina reforming catalysts such as Harshaw Mo 0602 and the Oronite molybdenum oxidealumina catalyst which contain only trace quantitles of silica do not appear to respond to the improvement of our invention.

The process is conducted as a continuous operation in which the naphtha feed after suitable prefractionation is preheated in a conventional fired heater to reaction temperature, mixed with recycle gases and passed through a fixed bed of the catalyst contained in a reaction vessel. Because of the endothermic nature of the reaction, it isadvantageously conducted in at least 2 reaction stages with intermediate reheating of the hydrocarbon stock. The reaction eflluent is passed to a separator where fixed gases are removed for recycle and oxygen addition. Liquid products from the separator are passed to a conventional fractionating system for recovery of the desired gasoline blending stocks. Although the reaction is conducted continuously, provision is usually made for periodic regeneration of the catalyst by burning off coke deposited on the catalyst surface in the usual manner by contacting with a regeneration gas containing dilute proportions of oxygen.

The process system is readily understood by reference to Figure 1 of the accompanying drawings which represents a simplified flow diagram of the process. The naphtha feed is charged to the system through line H) and fired heater II in which it is raised to the reaction temperature. Hot recycle gases from line [2 are mixed with the vaporized naphtha feed, and the mixture is charged to reactor [3 in a manner facilitating passage through a bed of the catalyst in tableted or pelleted form. The eflluent from reactor I3 is passed by means of line I4 through intermediate heater l5 and then is passed through reactor IS. The reactor efliuent from reactor I6 is passed through line I1 to separator [8, from which liquid products are removed by means of connection l9 to a fractionation system (not shown). Fixed gases recovered from separator I8 are recycled through the system through lines 20 and 2 i Excess tail gas may be removed from the systems through connection 22, and of course the gas separation system may comprise several stages for proper efficiency. Air or oxygen in controlled amounts according to our invention is added to the tail gas recycle in line 2! by means of connection 23. The recycle gas stream is recompressed in compressor 24 and reheated in recycle gas heater 25 before readmixture with the naptha feed in line [0.

A reaction temperature within the approximate range of 850 to 1000 F. is obtained by preheating the charge and by intermediate reheating between reactor stages. We have found, however, that the reforming is benefited by maintaining a temperature within the range of about 890 to 950 F. with a partial pressure of hydrogen corresponding 'to a hydrogen to hydrocarbon ratio of about 4 or 6/1. The total pressure may be in"the'r'ange of 5000 to 500 p. s'. i. g, the liquid hourly space velocity in the range of 0.5 to 4.0 and the hydrogen to hydrocarbon ratio may vary from about 2/1 to 8/1. The processing conditions are affected by the naphthenic content of the hydrocarbon stock t'obe processed. In general milder conditions are advantageously employed with stocks which are relatively high in content of naphthenes.

' The improvement in the yield-octane relationship"in reforming with 'a molybdenum oxidealihnina-silica catalyst according to our invention'is shown in Figure 2 of the graphic'ally accom'p'anying drawings. The" curves represent typical yield-octane data plotted for constant conditions with and without the presence of oxygen in the hydrogen ga's'stream charged to the reactor with'naphth'a feed." The naphtha feed tested as follows:

Gravity A. P. I 51.7 IBP, F .253 10% point, 9 F 273 50% point, F 306 90% point, F 352 E. R, F 392 Baraffins i- 57 .1 Qlefins 0.3 Naphthenes 1 -1 23.4 Aromatics e 19.2 Sulfur, wt. r 0.06 It. I 14,300 Bromine No 0.42

Octane numbers Research method neat 37.3

Research method 3 cc. TEL--. 54.4

Five tests were first made, using 0.5% air in hydrogen, about 4.5 hydrogen to hydrocarbon ratio, 750 and 1000 p. s. i. g. reaction pressure, 920 F. reaction temperature, and various space velocities. The tests in this series showed no effect of pressure on the yield-octane relationship.

.Changes in space velocity produced the expected relative shifts in the yield-octane relationship but introduced no overall change.

Three tests then were run using air-free hydrogen. The first of these tests following a series of air runs gave a yield-octane comparable to the air runs} indicating that the effect of air remains on the vcatalyst for a short time after switching to airfree hydrogen. The second and third tests on. air-free hydrogen gave a much less favorable yield-octane relationship as indicated by curve A of Figure 2.

After the air-free hydrogen tests, a test using 0.5% of air in hydrogen was made on this same catalyst charge. This test gave the same yieldoctane as previous air tests"; (curve B of Figure 2) showing that improved selectivity of the cat alyst can be restored almost immediately by switching to hydrogen containing air. Curve C of Figure 2 is based on comparable data with air addition in the case of a molybdenum oxidealumina catalyst containing only a trace of silica.

We claim:

1. In a process for reforming a petroleum hydrocarbon fraction boiling in the naphtha range in the presence of a molybdenum oxide reformin catalyst on alumina base containing a stabilizing proportion of silica and in the Presence of a hydrogen containing gas stream undercon ditions of about 850 to l0'00"F., about 500 to 1000 p. s. i. g., 0.5 to 4.0 liquid hourly space ve locity and a hydrogen to hydrocarbon ratio oi about 2/1 to 8/1, the step or" adding about 0.001 to 0.2% oxygen to the hydrogen containing gas stream.

2. The process of claim 1 in which the source of the oxygen is air. v 4

3. The process of claim 1 in which the percentage of oxygen added is about 0.1%."

4. The process of claim 1 in which the temperature condition is within the 'rangeof 890 to 950 F and the hydrogen to hydrocarbon feed rate is 4-6/1. r

LA VEBN H. BECKBERGER. RUDOLPH C. WOERNER.

References Cited i the file of this patent UNITED STATES PATENTS 

1. IN A PROCESS FOR REFORMING A PETROLEUM HYDROCARBON FRACTION BOILING IN THE NAPHTHA RANGE IN THE PRESENCE OF A MOLYBDENUM OXIDE REFORMING CATALYST ON ALUMINA BASE CONTAINING A STABILIZING PROPORTION OF SILICA AND IN THE PRESENCE OF A HYDROGEN CONTAINING GAS STREAM UNDER CONDITIONS OF ABOUT 850* TO 1000* F., ABOUT 500 TO 1000 P.S.I.G., 0.5 TO 4.0 LIQUID HOURLY SPACE VE- 